Electric furnace for the production of silicon and other materials having similar conditions of reaction



May 2l,- 1957 l. BEcKlUs n AL 2,793,242 ELECTRIC FURNACE FOR THE PRODUCTION 0F SILICON AND OTHER MATERIALS HAVING SIMILAR CONDITIONS OF REACTION Filed sept. 12, 1955 -z C tf 5y @Mw United States Patent O ELECTRIC FURNACE FOR THE PRODUCTION OF SILICON AND OTHER MATERIALS HAVING SIMILAR CONDITIONS OF REACTION Ivar Beckius and Hugo Lindstrm, Vasteras, Sweden, as-

signors to Allmnna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application September 12, 1955, Serial No. 533,537

4 Claims. (Cl. 13--27) Usually silicon is produced by reducing7 silica by aid of carbon, preferably in the form of charcoal. These materials are caused to react with each other by heating them to reaction temperature in an electric arc. The electric arc furnaces employed for this purpose are rather shallow and have larger horizontal dimensions. The temperature losses from the surface and from the environs of the electrodes are considerable. Furthermore silicon losses may occur due to the fact that the silicon produced at the high temperatures is allowed to evaporate. The occurrence of said losses is favoured by the relatively small height of the charge, by the craters formed around the arcs and by their high temperature. Also` the heat radiation from the furnace is so important that very unfavourable working conditions occur for the persons who are continuously charged with the service of the furnace.

The present invention relates to a new and improved furnace for the production of silicon and other materials having similar processes of reaction.

The principal feature of the invention is, that an electricinduction furnace is employed for the heat generation by inductive heating, and that the furnace has a body of relatively great axial length, which is divided by an especial arrangement of the turns of the primary winding, the power of which is adapted to be regulated into a charging and condensation zone, into a reaction zone, a collecting zone for the silicon produced and into a discharging zone, and that the furnace comprises a graphite cylinder serving as secondary winding for the heat generation in the charge, and an intermediate easily removable layer of heat resistant, heat insulating material between the primary winding and the graphite cylinder.

The charge consi-sts as usual of a mixture of quartz and carbon, which react when heated to l600-1800 C. thus creating silicon. This is collected within a colder zone below the reaction zone. The discharging zone below the collecting zone is also heated by induction so that the ow of the molten silicon can be regulated.

The accompanying drawing shows an embodiment of I the invention by way of example. Fig. 1 is a vertical section through the furnace and Fig. 2 shows a modication of the heating coil.

The graphite cylinder 1 bringing about the heat gen eration in the charge may be made of a tube of rings as shown on the upper part of the cylinder, or bricks as shown on the lower part thereof, and is surrounded by a layer 2 of heat insulating and resistant material. This layer consists preferably of powder, e. g. alumina (A1203), which is filled in from the upper part of the furnace and may be removed through an opening in its bottom. A coil 3 surrounds the middle part of the furnace and a further coil 4 surrounds its lower part. The furnace thus is divided into four zones with respect to its functioning: A rather cool charging and condensation zone A, a reaction zone B, a relatively cool collecting zone C. for `obtaining the desired reaction. The freezing point D. Thanks to this structural arrangement and the provision of said four zones the furnace has particularly favourable operation conditions. The charging zone may be made comparatively high so that the heat losses in the axial direction are inconsiderable. Due to said high charging zone it is also attained that silicon evaporated from the reaction zone is caused to condense in the upper part so that silicon losses are practically eliminated. In the zone B the temperature is held at l600-l800 C for obtaining the desired reaction. The freezing point of silicon lies at l450 C. If the temperature within the collecting zone is held somewhat above said temperature, it is likely that the temperature at the discharging opening 5 will become lower. The molten silicon therefore, would stilfen within said opening. For being able to discharge the molten charge and to regulate the discharging speed also the environs of the discharging opening is heated inductively by a coil 4 or by a part of the coil 3 (Fig. 2), the heating power of which coil may be regulated separately or together with that of the coil 3. On the drawing an alternative is shown wherein itis supposed that the temperature around the discharging opening is held so high, that the charge has no possibility to stitfen. In this case the discharging opening is closed during the melting process by a plug 6 which is removed when the molten charge is discharged. The coils 3 and 4 may be combined in a manner known per se to a single coil (Fig. 2) having different spaces between the individual turns for changing the density of current in the axial direction. The coils are surrounded by a magnetic shield 7.

rl`he construction as described allows for the graphite cylinder, a portion of which is consumed especially within the reaction zone, to be lowered toward the discharging part, so that the consumed portions may be replaced. Due to the fact that the intermediate layer is pulverulent it may easily be removed through an opening 8 thus facilitating the lowering of the graphite cylinder, the insertion of new graphite portions, or the exchange of the whole cylinder. 9 is a casing and 10 a Asupport for the furnace.

The new furnace is described for the production of silicon but it may also be used for the production of other materials having similar reaction conditions.

We claim as our invention:

l. A continuously working electric furnace for the production of silicon and other materials having similar reaction conditions, said furnace being an induction furnace having a furnace body of comparatively large axial length, comprising primary inducing means, means for regulating the heating power of said means, which inducing means is so arranged that the furnace is divided into a charging and condensation zone, a reaction zone, a collecting zone for the silicon produced in the latter zone, and a discharging zone, the furnace comprising a hollow graphite cylinder serving as secondary winding for the heat production in the furnace and an intermediate layer of heat resistant, heat insulating pulverulent removable material between the primary winding and the graphite cylinder, and an obturable discharge opening in the bottom of the furnace.

2. A continuously working electric furnace for the production of silicon and other materials having similar reaction conditions, said furnace being an induction furnace having a furnace body of comparatively large axial length, comprising primary inducing means, means for regulating the heating power of said means, which inducing means is so arranged that the furnace is divided into a charging and condensation zone, a reaction zone, a collecting zone for the silicon produced in the latter zone,

layer of heat resistant, heat insulating pulvernlentre-v movable material between the primary winding and the graphite cylinder, wherein the primary inducing means consists of a winding having Vdifferently spaced turns along the axial direction of the furnace body, and an obturable discharge opening in the bottom of the furnace.

3. A continuously working electric furnace for the production of silicon and other materials having similar reaction conditions, said furnace being an induction furnace having a furnace body of comparatively large axial length, comprising primary inducing means, means for regulating the heating power of said means, which inducing means is so arranged that the furnace is divided into a charging and condensation zone, a reaction zone, a collecting zone for vthe silicon produced in the latter zone, and-a discharging zone, the furnace comprising a hollow graphite cylinder serving as secondary winding for the heat production in the furnace and an intermediate layer ofiheat resistant, heat insulating \pulverulent removable material between the primary winding and the graphite cylinder, wherein the primary inducing means consists of two separate coils adapted for regulation, and an obturable discharge opening in the bottom of the furnace.

4. A continuously working electric furnace for the production of silicon and other materials having similar reaction conditions, said furnace being an induction furnace having a furnace body of comparatively large axial length, comprising primary inducing means, means for regulating the heating power of said means, which inducing means is so arranged that the furnace is divided into a charging and condensation zone, a reaction zone, a collecting zone for the silicon produced in the latter zone, and a discharging zone, the furnace comprising a hollow graphite cyiinder serving as secondary winding for the heat production in the furnace and an intermediate layer of heat resistant, heat insulating pulverulent removable material between the primary winding and the graphite cylinder, wherein the graphite cylinder is formed by ring-shaped parts, preferably composed of bricks, and an obturable discharge opening in the bottom of the furnace.

References Cited in the file of this patent UNITED STATES PATENTS Kistler Mar. 23, 1954 

1. A CONTINOUSLY WORKING ELECTRIC FURNACE FOR THE PRODUCTION OF SILICON AND OTHER MATERIALS HAVING SIMILAR REACTION CONDITIONS, SAID FURNACE BEING AN INDUCTION FURNACE HAVING A FURNACE BODY OF COMPARATIVELY LARGE AXIAL LENGTH, COMPRISING PRIMARY INDUCING MEANS, MEANS FOR REGULATING THE HEATING POWER OF SAID MEANS, WHICH INDUCING MEANS IS SO ARRANGED THAT THE FURNACE IS DIVIDED INTO A CHARGING AND CONDENSATION ZONE, A REACTION ZONE, A COLLECTING ZONE FOR THE SILICON PRODUCED IN THE LATTER ZONE, AND A DISCHARGING ZONE, THE FURNACE COMPRISING A HOLLOW GRAPHITE CYLINDER SERVING AS SECONDARY WINDING FOR THE HEAT PRODUCTION IN THE FURNACE AND AN INTERMEDIATE LAYER OF HEAT RESISTANT HEAT INSULATING PULVERULENT REMOVABLE MATERIAL BETWEEN THE PRIMARY WINDING AND THE GRAPHITE CYLINDER, AND AN OBTURABLE DISCHARGE OPENING IN THE BOTTOM OF THE FURNACE. 